Agriculture Reference
In-Depth Information
Members of the genus
Allium
are perennial, mostly bulbous, plants with:
●
underground storage organs: bulbs, rhizomes or swollen roots.
●
bulbs often on rhizomes, which can consist of the thickened basal sheaths
of leaf blades plus inner, thickened, bladeless 'true scales'or prophylls (as in
onion) or of just the thickened, bladeless prophylls (as in garlic)
surrounded by several membranous, dry skins.
●
rhizomes, which can be condensed or elongated and branched.
●
basal leaves arising from the underground stem; the leaves can have long,
concentric sheaths forming a false stem or 'pseudostem', as in leek.
●
bracts, often fused into a spathe that covers the developing inflorescence.
●
flowers borne in clusters of a loose few up to several hundred in a dense
inflorescence.
●
the individual flowers have a short stalk, are radially symmetrical, have
floral parts arranged in groups of three and the carpels develop above the
other flower parts.
●
the tepals and stamens both occur singly or as two whorls or three, the
inner whorl of stamens often being widened at the base; the flower colour
is mostly white or rose to violet, and occasionally blue or yellow.
●
the ovary has three cells (locules) with two or more ovules per locule; there
are often nectaries at the base of the ovary.
●
the style is single with a slender, or sometimes slightly swollen, stigma that
can have three lobes.
●
the seeds are globular to angular and black due to the phytomelan in the
epidermis.
●
the reserve carbohydrates are fructans, and many species release the
breakdown products of cysteine sulphoxides (CSOs) with their
characteristic smells (see Chapter 8) although this is often missing,
particularly in species of the the subgenus
Melanocrommyum
, to which the
largest number of ornamental species belong.
●
a basic chromosome number of eight is most common, but seven is found
in many of the subgenus
Amerallium
, many of which are native to North
America.
Infraspecific classification
The species of the Alliaceae have been grouped into various subgenera and
sections based initially on their visible features (Hanelt, 1990). In recent years
these groupings have been largely confirmed but refined using molecular
techniques, so that the relationships and phylogeny (family tree) of the
different species are becoming clearer (Fritsch and Friesen, 2002; Klaas and
Friesen, 2002; Friesen
et al.
, 2006).
Over time various processes cause differences in the nuclear, chloroplast
